Wind Loads on an Addition

[SteelPE]

I client who is looking to put a small addition onto an existing building. The existing building has dimensions of 130'x100'. The new addition has dimensions of 100'x40' (the 100' side will be placed against the 130' side of the existing). The addition is to frame independent of the existing structure.

My question is in regards to wind loads. In the past I have used the full wind loads when designing the addition. This seems a little harsh. How do others approach this issue, design for the full windward+leeward wind or design for windward wind and leeward wind separately?

 

[JAE]

I think you are referring to ASCE 7's reference that adjacent buildings cannot be utilized to screen off wind loads for lateral design.

My practice is to look at the two buildings and determine if there would ever be a chance that one building might someday be demolished, leaving the remaining building exposed to wind pressures in excess of its designed capacity.

In most cases the answer is yes, there is a possibility of demolition. It is hard to see how something like your example wouldn't apply to this.

In some cases, however, it does make sense such as where an independent truck dock section of a building is separated from a freezer warehouse by an expansion joint. It makes no sense to design the warehouse for the full wind when the truck dock is in its place. There would never be a freezer warehouse without the dock there, so we design for only wind exposed surfaces of the freezer.



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[DaveAtkins]

I disagree with JAE.

First, I can't think of an example where an owner tore down an original building, then closed off the open side of the remaining addition and called it a stand alone building. In theory, yes, this could happen, but I am hard pressed to think of an example.

Second, if this scenario occurred, the new engineer of record should be expected to verify the addition can stand on its own, and reinforce the addition if it cannot.

DaveAtkins

 

[JAE]

If the two buildings are owned by different entities then you'd have to design them as independent, non-screening buildings.
If the same owner for both - then DaveAtkins may have a point that the two "buildings" are essentially now the same singular building and limits wind exposure.

I'm just not so sure you can chrystal ball this and know that one of the two might not get demolished someday.
Owners are, more and more these days, not only re-purposing buildings but also altering our built environment to a very significant degree.

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[Ron247]

You need to make sure your building code does not explicitly state that "shielding" is not permitted. I am in a project right now where there are 4 separate buildings built side by side. They are combining 3 of them and going to tear down the 4th one. The 4th one is a perfectly good PEMB. Same Owner.

I always use full wind load for my projects like this.

 

[SteelPE]

Thank you for your comments.

I agree with most of what is said, however, there must be a few exceptions to providing the full wind on a structure (say if you were providing a new independently framed covered entrance to an existing building). In this instance, we are putting a small addition onto the side of an existing building. I can see an argument both ways, I just want to make sure I am am being efficient for the client.

FYI, this is an IBC 2015/ASCE7-10 project (sorry I didn't provide that information before.

 

[Once20036]

For what it's worth, if you were to design it for windward or leeward only, you`d need to include the effects of the internal pressure, GCpi.
I`ve found that this is often very similar to the windward + leeward, so your benefit of digging into this question might be minor.